In a conventional film deposition technique for OLED devices, it is common to use point evaporation sources. Nevertheless, the adopting of such point evaporation source can only be suitably applied in an evaporation process for forming thin films onto a small-size substrate, such as a piece of 370 mm×470 mm substrate, with a low material utilization rate ranged between 5% to 6%, and a low deposition rate of about 0.3 to 0.8 nm/s in a comparatively longer tact time, i.e. as long as 40 min to 50 min. Although there are already linear evaporation sources being adopted and used in some advanced evaporation processes, the shortcoming of low material utilization rate that is commonly seen in the process using point evaporation source still exists, despite that it had been improved from 5% in point evaporation sources to 20%˜50% in linear evaporation sources. In addition, in the early stage of a conventional evaporation process, not matter it is using a point evaporation source or a linear evaporation source, the evaporation source must be shielded and covered by a shutter. Since in the early stage the powder-like or granular-like evaporation material is just started being heated and thus the evaporation process is in a transient period when the consequent vapor flow rate is increasing gradually, the vapor flow that is increasing can cause unstable film deposition rate which will eventually cause film to be formed non-uniformly on the substrate. Therefore, at early stage of an evaporation process, the evaporation source should be shielded and covered until an equilibrium vapor saturation has been reached and thereby the resulting deposition rate is stabled, that is when the shutter can be opened for enabling an evaporation process.
For an evaporation technique of large-area thin film deposition, no matter it is using a point evaporation source or a linear evaporation source, the cosine law of distribution angle must be considered as the larger the substrate to be deposited is, the larger the distance between the evaporation source and the substrate should be. In addition, the size of the shutter is increased to cope with the larger substrate. For instance, for performing an evaporation process on a substrate that is longer than 1 meter, the distance between the used evaporation source and the substrate must be over 1 meter. Consequently, the film can still be deposited on the substrate non-uniformly as it can take too long for the one-meter-long substrate to travel passing the deposition chamber during the shutter is being activated to open and close in a reciprocation manner.